This invention relates to a circular saw blade.
Diamond blades are used to cut a variety of hard, abrasive, difficult-to-cut materials, such as concrete, stone, asphalt, and brick. The cutting portion of the blade, called a xe2x80x9csegmentxe2x80x9d is comprised of diamond abrasive grit particles held in place by a metallic matrix or xe2x80x9cbond.xe2x80x9d In use, the diamond abrasive grit particles act like tiny cutting points; they are forced through the material being cut by the power of the saw machine, causing fracture of the parent material which produces the cutting action. As the diamond abrasive particles do the work, they slowly wear away and become dull or fractured. For the blade to keep cutting, the bond material must also wear away to expose new diamond particles. If the bond and diamond are correctly designed and matched to the material being cut, the blade will continue to cut until the entire segment is worn away.
There are two primary performance measures for a diamond blade:
1. Lifexe2x80x94how much cutting can be done before the segment is gone; measured in inch-feet or square inches of cut. Life will vary depending on the material being cut.
2. Speed of Cutxe2x80x94how quickly the blade moves through the material; measured in inch-feet per minute or square inches per minute. Speed of cut also varies with the material being cut.
Increased life is typically achieved by using a bond material that is more wear resistant and/or increasing the amount (concentration) of diamond grit. Increased speed of cut is typically achieved by using a xe2x80x9csofterxe2x80x9d or faster wearing bond material and/or decreasing the amount (concentration) of diamond grit. Thus these two performance requirements compete with each otherxe2x80x94to get longer life one must give up speed of cut, and vice-versa. This trade-off is generally accepted by the industry. However, the invention is a break-through in that it achieves increased speed of cut without sacrificing life through the physical design of the blade geometry.
This invention includes the geometry and spacing of the slots and segments around the periphery of a circular cut-off saw blade. The slots are designed to produce maximum airflow and cooling of the saw in use. The segments are designed to work with the slots to maximize the airflow and cooling effect of the slots. This blade design is intended primarily for dry-cutting applications. It may also offer advantages for wet-cutting applications.
Design features of the slots include the curvature of the slot and the angle of the outer opening of the slot with respect to a radial line. The radius of curvature of the slots generally ranges from 1xe2x80x3 to 3xe2x80x3. The curvature of the slots is optimized to work with a specific combination of saw diameter, number of slots/segments, saw operating speed, and other design parameters to produce the maximum airflow and cooling. The curvature of the slot imparts more energy to the surrounding fluid (air) than does a straight slot.
The curvature and angle of the slots works with the rotation of the blade to produce outward airflow. There are many variations of the various parameters of the slot design. The slots may open to the periphery of the blade at an angle with respect to a radial line of from about 0xc2x0 to about 30xc2x0. The center of curvature of the slots is preferably ahead of the leading edge of the sidewall relative to the correct direction of rotation of the saw blade, but is alternatively behind the leading edge. The direction of rotation works with the angle and curvature of the slots to produce outward airflow. This orientation of slots also produces a more stable blade during cutting. Other variations include the number of slots (preferably from 4-75); the width of the slots (preferably from about 0.125xe2x80x3 to about 0.250xe2x80x3); the depth/length of the slots (preferably from about 0.5xe2x80x3 to about 2xe2x80x3); the radius of curvature of the slots (preferably from about 1xe2x80x3 to about 3xe2x80x3); and the use of more than one slot configuration on the same blade (for example, a mixture of longer and shorter or narrower and wider slots).
In the preferred embodiment of the invention, the curvature of the slots is such that as the blade advances (rotates) into static air, the innermost portion of the slot advances first, and is curved so that the direction of the slot is close to parallel with the direction it is traveling relative to the air. The air flows into the slot to fill the vacuum that would otherwise occupy the slot. As the blade continues to advance, the angle of the slot gradually changes toward a more radial angle; and the air is accelerated in a progressively more radial direction. Finally, as the slot exits the steel, the direction of the slot is radial, and the direction of the air flow is nearly radial.
Of the total circumference of the blade, a portion is covered by segments and a portion is used by the slots. The segments are in contact with the workpiece; in the slot area there is no contact. The total contact area can be expressed as a portion or percentage of the total peripheral area. Typical contact area values are in the range of 80-90% (of the full circumference). Blades with a lower contact area (in the range of 80-85% or less) typically act xe2x80x9csofterxe2x80x9d, meaning that they cut faster and wear quicker, all other things being equal. Conversely, blades with a higher contact area (85-90% or above) typically act xe2x80x9charderxe2x80x9d, meaning that they cut slower and wear faster. With the lower contact area, there is more power per square inch of cutting area applied by the machine; this results in higher load per abrasive particle, which makes that particle bite into the work-piece more, but it also causes the abrasive to wear and break-down faster.
The preferred configuration of the inventive blade is toward the low end of the xe2x80x9cconventionalxe2x80x9d range on peripheral contact areaxe2x80x94approximately 80%. By keeping the peripheral contact area toward the low end of the range, there is a good amount of room for slots. The bigger the slot, the more air it can move. However, if the slots are too big, the peripheral area is too low, and the blade will wear too quickly. The aim is to have enough area for good life, and also achieve fast cut. Accordingly, in one respect, the size of the slots is optimized to give the best blend of a large slot for air-flow combined with adequate peripheral contact area for blade life.
The length and curvature of the slot is also optimized to give the largest slot possible without reducing the strength and stiffness of the core below an acceptable level. Obviously, the more material that is removed by making the slot larger, the weaker and more flexible the core will become. The preferred inventive design is a compromise on size of the slot versus strength and stiffness of the core.
The number and size (length) of the segments is also optimized to give fast cut, with efficient flushing of fines, without inducing excessively fast wear or choppy cut. Standard segment lengths that are common in the diamond blade industry are 2 inches (50 mm) and 40 mm (1.575 inch), though a wide variety of segment lengths have been used. Shorter segments can be used to reduce the peripheral area and increase the speed of cut; the tradeoff is shorter blade life and a xe2x80x9cchoppyxe2x80x9d cut if the slots between the segments are excessively large. The length of the segments of the preferred embodiment herein is 1.250 inches, which provides for a high number of segments to yield the correct peripheral area and slots that are big enough to give the desired airflow effect without being so large as to produce a choppy cut. Variations contemplate segments in the 1.000-1.500 inch length range.
The invention also includes cutting segments in which the angle on the end of the segments is aligned either with radii of the blade (i.e., straight-edged segments), or aligned with the angle of the slot at the periphery, so that the edges of the segment effectively continue the slot sidewalls. There can be from 4 to 75 segments, depending on the blade diameter and the number of slots. Each segment is from about 1xe2x80x3 to about 2xe2x80x3 long. The invention can apply to blades having a nominal diameter of from about 4xe2x80x3 to about 36xe2x80x3.
The invention provides several operating advantages, including:
1. Cooler operation: The airflow cools the segments and the product being cut. This inhibits heat-induced damage to the diamond superabrasive, which would otherwise degrade the diamond particles and cause the blade to stop cutting. Current diamond blades perform very poorly in certain applications where a lot of heat is generated; and cooler-running blades generally cut faster and last longer.
2. Removal of fines: The increased airflow produces more effective removal of the fine material in the cut. Removal of the fines gives the diamond abrasive more direct contact with the parent material, which produces better cutting action. This results in faster cutting and/or longer blade life.
3. Longer blade life: The cooler running and better removal of fines make the blades last longer. This is particularly true in demanding applications where heat buildup and/or fines buildup are problems.
4. Faster cutting: The cooler running allows lower grade diamond to be used in the segments without fear of thermal degradation; lower grade diamond generally produces a faster cut.
5. Audible warning if mounted backwards: The curved slots make a different sound when operated in the opposite rotating direction; the sound of a blade that is mounted backwards is distinguishable from one that is mounted correctly.
6. Unique appearance: The design of the blade provides a unique appearance which makes the blades more easily visually distinguished from existing blades, which provides a clear product identity.